1. Field of the Invention
The present invention relates to a laminated glass product which is prepared by bonding two or more glass substrates by inserting a photocurable composition comprising a polyene, a polythiol and a photocuring rate accelerator and irradiating it by active rays to cure the composition.
2. Description of the Prior Arts
A laminated glass product has been used for various usages including safety glass plates for car and optical glass products.
Various processes for preparing a laminated glass product have been proposed.
For example, a laminated safety glass plate has been prepared by inserting an organic polymer film between a pair of glass plates and bonding them at an elevated temperature under an elevated pressure. In order to bond uniformly the pair of glass plates without any distortion, a complicated and time-consuming operation has been required.
Polyvinylbutyral film has been usually used as the organic polymer film for a laminated safety glass plate. A polyvinylbutyral film having a thickness of 0.2 to 1.0 mm is treated by an embossing roll and then, it is washed and dried and the film is held between a pair of glass plates and they are bonded at about 100.degree. C. under an elevated pressure to perform a preliminary adhesion and deforming and then, they are heated in an autoclave at 120.degree. to 150.degree. C. under a pressure of 10 to 15 Kg/cm.sup.2 to perform a final adhesion. A large size apparatus is required for this process, and a long operation time such as 2 hours is required in this process.
It is impossible to combine a process for preparing laminated safety glass plates in a continuous process for producing a glass sheet when said process is employed. Accordingly, a laminated safety glass plate has been used only for special usages. In order to improve the process, various studies have been carried out for preparing laminated safety glass plates by feeding a liquid resin and curing it to bond glass plates.
When a liquid resin such as alkyd resins, polyurethane resins is used, there has been found various disadvantages that a transparency of the cured composition is not satisfactory, a cured composition is brittle at room temperature and the product could not be used as a laminated safety glass plate in commercial.
It has been studied to bond glass plates with a photocurable composition comprising an ethylenically unsaturated compound or an unsaturated polyester as a main component in a photocuring method. However, such photocurable compositions have disadvatages that a curing time is too long; or a contraction is remarkably high in the curing step; or an imcomplete curing is caused by oxygen in air; or a coloring is caused by exposing it by ultraviolet rays, and accordingly, it has been difficult to prepare a laminated safety glass plate which can be practically used.
An optical glass product has been prepared by bonding glass substrates with a bonding agent.
The following properties are usually required as a bonding agent for preparing an optical glass product.
(1) colorless and transparent; no absorption nor scatter; PA0 (2) no fluorescent property; PA0 (3) refrative index being similar to that of an optical glass; PA0 (4) high bonding strength which is not changed in aging; PA0 (5) durable to heating, freezing, vibration, oil or solvent; PA0 (6) bonded surface being durable in variation of volume of bonding agent laver in curing or in chemical reaction; and PA0 (7) high processability.
It has been known to use Canada balsam, epoxy resins, polyvinylbutyrals, polyesters and cyanoacrylate resins as a bonding agent for preparing an optical glass product. These bonding agents had certain disadvantage on its processability and its property.
Canada balsam and polyvinylbutyrals are thermoplastic bonding agents whereby a temperature in a usage is limited and a distortion in contraction of the bonding agent layer caused by heating should be eliminated to require a long time for the step.
Epoxy resins are usually used by weighing and mixing with an amine type hardener to have low processability.
Polyester resins have high contraction efficiency in a polymerization whereby a product is affected by moisture in a condition of high temperature and high moisture to peel off from a peripheral part of the product.
Cyano-acrylate type bonding agents have been used, but are not suitable for a wide area.
It has been known that a mixture of a polyene and a polythiol is cured by irradiating ultraviolet rays, in the presence or in the absence of a photocuring rate accelerator (Organic Reaction Vol. 13, page 165-376 (1963)). However, such mixture has not been considered to prepare a laminated glass product.
A photocurable composition comprising an unsaturated compound in a radical polymerization system has been used for preparing a laminated glass product in Japanese Patent Publication No. 30954/1971 and Japanese Unexamined Patent Publication No. 1035/1973. This has disadvantages that an inferrior curing caused in the presence of air and a squeezed part of the composition should be washed out.